1. Field of the Invention
The present invention relates to graphite oxide coated particulate materials (such as graphite oxide coated sand), methods of manufacture of such materials, and uses thereof.
2. Background of the Invention
Graphene is a flat, sp2 hybridized, two-dimensional (2D), honeycomb arrangement of carbon atoms with single carbon atom thickness. Graphene is expected to have far reaching consequences in not only understanding the fundamental aspects of these materials but also realizing real time applications. [Park 2009].
Graphene oxide is single to few layers of graphite that contains several oxygen rich functional groups rendering it soluble in water. Production of graphene through wet chemical oxidation of graphite to graphite oxide (GO) has become a popular method and a primary factor for an overwhelming interest in this new material. The oxygenated functional groups such as carboxylates, lactols and epoxides primarily lie at the edge of the nanographite sheets while the basal planes contain predominantly sp2 hybridized graphene-domains. While the oxygen functional groups impart hydrophilicity, the graphene domains render hydrophobic character to these ampiphilic GO particles. [Kim 2010]. Consequently, GO is soluble in several polar and non-polar solvents including water but suffer from breakdown of electrical conductivity. [Li 2008]. The conductivity can be restored to a certain extent by thermal or chemical reduction of the oxygen functionalities, although such treatments also increase the hydrophobicity. [Gao 2009]. Nevertheless, the intrinsically large surface area of GO have found niche in electrochemical energy storage devices, hydrogen storage, and catalysis. [Stoller 2008; Dimitrakakis 2008; Dreyer 2010].
Historically, water purification technologies have utilized high surface area carbon materials in the form of activated carbon for decolorization and heavy metal ion retention. [Santos 2007; Mohan 2000]. The plethora of functional groups and the strong van der Waals interaction allows adsorption of heavy metal ions as well as organics. Therefore, they have found applications, among others, in water and air purification for heavy metal removal, trace organics, decolorization, and odor removal. Typically they are synthesized from waste materials by high temperature (1000-1700° C.) pyrolysis. It is also to be recognized that in most adsorption applications, they are used in the form of hundreds of micron or milli-meter scale granules; however, only the surface layer are typically utilized for these separation—the bulk of the material in the granules remains unutilized due to diffusion limitations. It is of interest to develop novel granular adsorbents which are inexpensive, does not require any high temperature process, yet are functional to the same extent as the commercial grade activated carbon.
Compared to these materials, GO is produced by room temperature soft-chemistry principles and is likely to be cost-efficient. Only recently has a report on magnetite-graphite hybrid materials for magnetically controlled speciation of arsenic from water been published. [Chandra 2010]. The possibility of harnessing this readily available and inexpensive material has been relatively unexplored.